Neural Mechanisms Mediating the Effects of Food Cues and Acute Exercise: a functional Magnetic Resonance Imaging and Functional Connectivity Investigation

摘要

The obesity epidemic is imposing enormous costs on individuals and on developed and developing societies. Ultimately, obesity arises from a sustained imbalance in the energy balance equation from either excessive energy consumption or significantly reduced activity. Here we report on findings from two fRMI studies, each of which examines one side of the energy balance equation. In our first study, the Passive Viewing of Foods, we examined the effects of acute exercise on self-report measures of appetite suppression and on neural activity resulting when normal BMI subjects viewed blocks of high calorie or low calorie food cues. We found that acute exercise suppressed self-reported appetite and reduced the activation of two key brain areas relative to appetite regulation: the dorsal anterior cingulate (dorsal ACC), a frontal attention processing area, and the nucleus accumbens, a central reward processing area. Moreover, we conducted functional connectivity analysis to examine other areas of the brain that were positively or negatively correlated with these two areas when viewing high calorie food cues following exercise. The functional network identified was broadly distributed and included increased coupling with the putamen, insula, operculae, inferior frontal gyrus, and superior parietal lobule and decreased coupling with the amygdala and orbital frontal cortex, among other areas. We believe this is the first study of exercise induced appetite suppression that used whole brain analysis and functional connectivity to show both absolute reductions of activity in the dorsal ACC and nucleus accumbens as well as a distributed functional network with differential coupling and de-coupling. These findings help identify a functional network that mediates appetite suppression as a result of acute exercise. In our second study, the Categorical Food Stroop, we deploy a novel Stroop-like paradigm that used the same high and low calorie food cue exemplars to examine the effects of the food cues on cognitive interference and the cognitive control effect of conflict adaptation. In the study, subjects categorized the high and low calorie food cue word targets, which were overlain on veridical images of the same food cue exemplars. Relative to interference, we observed that normal BMI subjects took 18 ms longer to categorize high calorie words overlain on low calorie images (high calorie incongruent trial) than they did to categorize low calorie words on high calorie distractors (low calorie incongruent trial). Relative to conflict adaptation, a measure of cognitive control over response inhibition when there are conflicting response options, we observed a significant overall effect of conflict adaptation but then showed that only one calorie characteristic (high calorie incongruent trials following high calorie incongruent trials, HH trials) was significantly contributing to the overall conflict adaptation. To our knowledge, this was the first categorical food Stroop and the first study to identify the role of caloric characteristic in modulating cognitive control relative to response selection in food-related decisions. Our neural observations showed that the increased interference in incongruent trials is associated with activation in the supramarginal gyrus, superior parietal lobule and the superior lateral occipital cortex. The high cognitive control HH trials compared to the low cognitive control trials activated the parahippocampal gyrus, the right amygdala, the orbital frontal cortex, the superior parietal lobule, the angular gyrus, and temporal-occipital gyrus. The parahippocampal gyrus and superior parietal lobule were used as seeds in functional connectivity analysis and revealed a high degree of overlap in their distributed functional networks mediating high cognitive control trials. The findings shed new light on both the high calorie stimulus specificity of cognitive control in normal subjects and the distributed functional network that mediates the effects of the cognitive control in food related decisions.